The present invention relates to electrical data printers and more particularly to a novel thermal print head assembly for forming characters preferably upon a temperature sensitive impression medium in a dot-matrix type line printer.
It is well-known in the line printer art to use a print wire actuated by a solenoid to impinge upon an inked ribbon to form a dot upon a paper document, such as a sheet of paper. An advanced form of line printer utilizes a plurality of such print wires arranged along a straight line substantially parallel to an edge of the paper to simultaneously print a column containing a first number of dots; the print head containing the plurality of print wires and their actuating solenoids is moved across the paper to print a plurality of dot columns (typically five in number) to form a dot matrix pattern representing a character, number, symbol, or segmented pattern. Characters, numerals and symbols are typically formed within a 5 .times. 7 dot matrix. Lines of characters are formed in this manner.
In a typical application, a line usually consists of either 80 or 132 characters; each character consisting of 5 dot columns, each column containing typically seven dots. In such a dot-matrix line printer, the inked ribbon must be positioned to be impacted by all seven print wires. Each print wire impacts the inked ribbon a large number of times for each line, e.g. a total of 400 possible impacts for an 80 column line printer. The inked ribbon is thus subjected to rapid wearing and deterioration. As the inked ribbon wears the sharpness of dots is significantly reduced. The proper sharpness of dot patterns, therefore, requires that the ribbon either be re-inked at frequent intervals -- a process unduly messy and complicated -- or that the ribbon be changed at frequent intervals -- a time consuming process requiring removal of the line printer from active service.